Missing "Thingies" in Firefox

On many websites (including RV ones and thus the relevance here;)), Firefox doesn't show "thingies" that are buttons you can click on to go to a place within the site. The square is there but instead of a picture, it shows a couple of letters and numbers. It doesn't do it for all sites, but many.

I've tried to search for solutions in Firefox forums but don't know what they are called. Icons gets solutions that are not relevant. Anyone know what I'm talking about? I don't:h